(1) Field of the Invention
The present invention relates to a luminous display device which reflects light of a display image emitted from a liquid crystal display by means of transmission of illumination light from a backlight so as to provide the reflected light to be seen.
(2) Description of the Related Art
So far, for example in a vehicle, in order to make a driver see various information by superposing on a view in front of a windshield, a head-up display has been used, in which light of a display image from a liquid crystal display in a dash-board is reflected to the side of the driver by the windshield or a combiner arranged on this side of the windshield, so that a virtual image of the display image can be seen on the windshield or the combiner.
Further, in a vehicle, in some cases, in order to lighten the burden imposed on driver's eyes due to a large change in a focal distance during eye motion upon traveling of the vehicle, information displayed as a real image by a combination meter is subjected to be seen with a display device of a virtual image display type.
In such a display device of a virtual image display type, light of a display image from a liquid crystal display is reflected once or a plurality of times by a reflecting mirror in a dash-board, then the reflected light is subjected to be seen by a driver. By elongating an optical path with the reflection of the light by the reflecting mirror, the focal distance is brought close to a focal distance when a front view through a windshield is seen.
In the display devices described above, since the windshield, combiner and reflecting mirror for reflecting the light of the display image are arranged with an inclination to a line of sight from the driver to the liquid crystal display, therefore in order to prevent the virtual image to be seen by the driver from inclining and being seen distorted due to a gap of the optical path from the driver to the liquid crystal display generated between the upper side and the lower side of the display image, the liquid crystal display is arranged with an inclination to the line of sight from the driver to the liquid crystal display.
Moreover, another reason why the liquid crystal display is arranged with an inclination to the line of sight from the driver to the liquid crystal display is to prevent that external light such as sun light entered into a vehicle through the windshield reaches the liquid crystal display and its reflected light reaches eyes of the driver together with the light of the display image (for example, Japanese Patent Application Laid-Open No. 2000-56254.
Generally, light of an image emitted from a liquid crystal display is divergent light having an optical axis having a direction perpendicular to a display surface of the liquid crystal display because a backlight is arranged in parallel with the liquid crystal display.
Therefore, if the liquid crystal display is arranged with an inclination to the line of sight from the driver to the liquid crystal display, an irradiation range of the light of an image from the liquid crystal display is deviated with respect to a layout of the reflecting members such as the windshield, combiner and reflecting mirror, which are located on the line of sight.
Such a deviation makes a part of the light of an image run off to the outside of the reflecting members, causing an insufficient amount of light of the display image. Therefore, it is necessary to arrange the liquid crystal display and the backlight close to the direction perpendicular to the line of sight as much as possible so that all of the light of an image is irradiated to the inside of the reflecting members.
However, if the liquid crystal display and the backlight are arranged in such a manner as described above, a gap of the optical path from the backlight to the driver between the upper side and the lower side of the display image is generated, so that a difference takes place in a degree of attenuation in the light of an image, causing generation of nonuniformity in brightness for the virtual image of the display image, which is seen by the driver.